1. Field of the Invention
The invention relates to an overvoltage protection device for protecting electrical low voltage installations, with a lower device part and at least one upper device part, the lower device part having input and output terminals for electrical conductors and contact elements which are connected to the input and output terminals and which are made especially as plug sockets, and the upper device part having at least one protection element.
2. Description of Related Art
Electrical circuits normally work free of noise with the voltage which is specified for it, i.e., the rated voltage. This does not apply when overvoltages occur. Overvoltages are all voltages which are above the upper tolerance limit of the rated voltage. They also include mainly transient overvoltages which can occur due to atmospheric discharges, as well as due to switching operations or short circuits in power supply networks and can be coupled conductively, inductively or capacitively into electrical circuits. In order to protect electrical or electronic circuits, especially electronic measurement, control and switching circuits against transient overvoltages, overvoltage protection elements which capture and limit overvoltage peaks have been developed and have been known for many years.
The required measures for protection of the power supply of installations and devices are classified into various stages depending on the choice of arresters and the ambient influences which can be expected. The overvoltage protection devices for the individual stages differ by the level of the discharge capacity and the protection level.
The first protection stage (type 1) is generally formed by a lightning stroke current arrester which is installed as an extremely powerful protection device in the central power supply of a building. An important component of such a lightning stroke current arrester is a spark gap with at least two electrodes, when the spark gap is struck an arc forming between the two electrodes.
The second protection stage (type 2) generally forms a varistor-based surge arrester. The protection stage again limits the remaining residual voltage via the lightning stroke current arrester. Depending on the risk potential of the installation which is to be protected or of the building which is to be protected, in the individual case it can be sufficient if the second protection stage is started.
The third protection stage (type 3) is called apparatus protection and is generally installed directly upstream of the device which is to be protected. With the apparatus protection a residual voltage which is safe for the connected device is achieved. These overvoltage protection devices exist in different designs, especially also as switchgear cabinet module.
In MSR technology, as a result of the high sensitivity to overvoltages the overvoltage protection devices often have overvoltage protection elements with combined protective circuits, one overvoltage limiting component being used for coarse protection and one overvoltage limiting component being used for fine protection. The components which can be especially gas-filled surge arresters, spark gaps, varistors or suppressor diodes are often connected indirectly in parallel, between the overvoltage protection elements there being longitudinal elements as decoupling resistors which must be adapted to the respective protective circuit, i.e., to the overvoltage protection elements used.
This invention is used especially in overvoltage protection devices which are used for apparatus protection and which are made as a switchgear cabinet module. However, the invention is not limited thereto and can be implemented fundamentally also in overvoltage protection devices of type 1 or of type 2.
For reasons of modularity and flexibility and to facilitate repair efforts, switchgear cabinet modules are often made in at least two parts, one of which is a permanently installed base element as a lower device part and the other is comprised of at least one interchangeable protective plug as an upper device part. The base element is used to fasten an overvoltage protection device on a mounting rail and to connect the individual electrical conductors, for which the base element has corresponding input and output terminals, which can be made in any connection technology, for example, screw terminals, tension spring terminals, direct clamp-type terminals, or quick connect terminals. Depending on the version, this overvoltage protection device can be made as two-wire, three-wire or four-wire protection. The protective plug has the actual overvoltage protection circuit with the overvoltage protection element or elements which are matched to the respective application. Fundamentally two or more protective plugs can also be plugged onto a corresponding wide base element next to one another in the longitudinal direction of the mounting rail.
To easily make mechanical and electrical contact of the lower device part with the respective upper device part, the lower device part has plug sockets connected to the terminals and the upper device part has corresponding plug pins so that the upper device part can be plugged onto the lower device part without tools. In addition, the known overvoltage protection device has another changeover contact as transducer for remote reporting of the state of at least one protection element, as a result of which comfortable remote monitoring is possible. Moreover, for example, German Utility Model DE 20 2004 006 227 U1 and corresponding U.S. Pat. No. 7,411,769 B2 disclose that the upper device part has an optical state display which can be mechanically actuated. In this way, the state of the overvoltage protection device can also be easily read off directly on the device.
An overvoltage protection device underlying the invention has already been fundamentally described in German Patent DE 33 46 753 C2. This type of overvoltage protection device has been marketed for many years by the assignee of the present application under the product name “PLUGTRAB PT” (see, Phoenix Contact brochure “Overvoltage Protection TRABTECH 2007, pages 60 and 61). One important feature of this overvoltage protection device is the possibility of being able to insert and withdraw individual protective plugs in an impedance-neutral manner, as a result of which sensitive signal circuits, such as for example, terminal measurements or bus systems, are not influenced when the protective plug is replaced. For this purpose, in the lower device part, there are longitudinal elements, especially decoupling resistors, in the line paths which run continuously between input and output terminals which are assigned to one another. Since the base element also remains installed in the through wiring when the protective plug is replaced, interrupt-free and impedance-neutral withdrawal and insertion of the protective plug for test and replacement purposes are thus possible.
Even if the aforementioned overvoltage protection devices have greatly proven themselves in practice, they have the disadvantage that, not only are a plurality of protective plugs matched to the respective application, but also a large number of different base elements must be made available which have longitudinal elements which are matched to the protection circuit which is located in the protective plug. The number of base parts which are to be made available by the manufacturer of the overvoltage protection devices in the prior art is reduced in that the longitudinal elements are also integrated in the plug-in upper device part; but this results in that the impedance of the electric circuit or signal circuit is changed when the protective plug is inserted and withdrawn.